API: is it possible to save a variable's value for pose space deformations?
Thanks to Leander's comment about custom properties to help me get on the right track.

There is the custom properties subsection in the object tab (found in the properties window). Most of us may be familiar with it, as it is fundamental to doing things such as controlling multiple shape keys or other effects. At the time I knew about these, but not as much as I thought. I didn't want to use these at first because I didn't want the rig's custom properties section to get filled up with a bunch of junk, since I feel that areas should be reserved for users. But since Leander suggested such a thing could be done with code, I looked into the topic further, now searching "properties" as my keyword, to see if I could manage to do this in a discrete way.

https://docs.blender.org/api/2.79/bpy.props.html
- "Custom properties can be added to any subclass of an ID, Bone and PoseBone."

At the mention of custom properties being used for bones as well, I looked and found that indeed, there is a hidden custom properties subsection for each individual bone. This is great because: 1 I can't think of any user who would need to go into this section, to manage custom properties per bone, so this stuff should, for the most part, stay out of users' way; 2 it helps perfectly organize where my data should be found, making the coding a bit easier.